Porous Ceramic Paving Material

ABSTRACT

The disclosure is directed to a method of constructing a porous, ceramic pavement that is permeable to aqueous fluids and more resistant to acidic rainwater than concrete. The method includes selecting a porous, ceramic paving material having a compressive strength sufficient for a particular use of a surface to be paved. A base material can be selected to serve as a support for the paving material, wherein the base material is permeable to aqueous fluids. The base material is applied to the surface to be paved, and the paving material is positioned on top of the base material to provide a porous, ceramic pavement.

CROSS REFERENCE

This application is a divisional of U.S. patent application Ser. No.11/318,005, filed Dec. 23, 2005, which claims priority to U.S. patentapplication No. 60/676,598, filed Apr. 29, 2005, both of which areincorporated by reference.

BACKGROUND

1. Field of the Invention

This invention is directed to methods of making and using pavingmaterials and, more specifically, a novel porous, ceramic pavingmaterial.

2. Description of the State of the Art

Human development has taken away much of our natural areas. Theprevalence of impermeable paving on developed land has led to a decreasein groundwater recharge and an increased risk of contamination, asrunoff from rain washes surface pollutants directly into our waterways.Furthermore, this high flow rate of runoff can also result in anincrease in erosion.

To combat this problem, traditional pavers have been installed with gapsfor water to seep through, but this creates safety and accessibilityissues as well as the need for an additional material, such as grass orsand, to fill the gaps. Traditional pavers are also often made from aconcrete-based material and, unfortunately, concrete suffers degradationfrom rainwater, since rainwater is often acidic. As a result, a porousconcrete that is permeable to rainwater is destined to fail under suchconditions, and society is forced to use substantially impermeableconcrete systems instead and suffer the consequences.

Accordingly, an improved paving material that is not only strong enoughto serve as a paving material in a range of applications, but is alsopermeable to aqueous fluids and resistant to chemical degradation, canprovide a benefit to society by allowing our land to get the rainwaterit needs and creating less pollution and erosion from run-off problemsthat exist with currently used materials.

SUMMARY

Embodiments of the present generally encompass porous, ceramic pavingmaterials. In some embodiments, the invention is a porous, ceramicpaving material comprising a heat-treated component comprising a metaloxide and a filler material, wherein the filler material contributes tothe porosity of the paving material, and the paving material ispermeable to aqueous fluids and more resistant to acidic rainwater thanconcrete.

In some embodiments, the invention is a method of creating the porous,ceramic paving material. The method includes preparing a compositioncomprising a metal oxide and a filler material, and the preparingincludes selecting the filler material to provide a desired porosity tothe paving material. The filler material is mixed with the metal oxide,and the composition is formed into a desired shape by applying pressureto the composition in a mold. The formed composition is thenheat-treated to create the porous, ceramic paving material, wherein thepaving material is permeable to aqueous fluids and more resistant toacidic rainwater than concrete.

In some embodiments, the invention is a method of constructing a porous,ceramic pavement. The method includes selecting a porous, ceramic pavingmaterial having a compressive strength sufficient for a particular useof a surface to be paved. A base material can be selected to serve as asupport for the paving material, wherein the base material is permeableto aqueous fluids. The base material is applied to the surface to bepaved, and the paving material is positioned on top of the base materialto provide a porous, ceramic pavement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method of making porous, ceramic paving materialsaccording to some embodiments of the present invention.

FIGS. 2A and 2B illustrate shapes that may be desirable according tosome embodiments of the present invention.

FIG. 3 illustrates a method of constructing a porous, ceramic pavementaccording to some embodiments of the present invention.

DETAILED DESCRIPTION

As discussed in more detail below, the embodiments of the presentinvention generally encompass porous, ceramic paving materials. The“paving material” can include a material that provides a hardened,treated, or finished surface that may be exposed to the wear of trafficthat can include foot traffic or vehicle traffic. Generally speaking,the paving material of the present invention includes a ceramic coveringfor any surface that can benefit from an improved durability and,particularly, those surfaces that can benefit from an added feature ofpermeability to aqueous solutions, such as rainwater. The teachingprovided below is directed to making and using these novel porous,ceramic paving materials.

FIG. 1 illustrates a method of making porous, ceramic paving materialsaccording to some embodiments of the present invention. The porous,ceramic paving materials of the present invention are made by preparing101 a composition comprising a metal oxide and a filler material. Thepreparing includes carefully selecting 102 a filler material to assistin producing the desired porosity in the paving material. The metaloxide and filler material are mixed together to form the composition.The composition is then formed 103 into a desired shape by carefullyselecting 104 and applying 105 pressure to the composition in a mold. Avirtually infinite number of shapes and designs can be formed. A finalstep in the process is heat-treating 106 the shaped composition tocreate the porous, ceramic paving material, wherein the heat-treatingincludes carefully selecting 107 the temperature of the treatment forcontrol over physical properties of the paving moldule, such as porestructure and strength, and applying 108 the temperature for apredetermined amount of time. A finishing step 109 can also be used insome embodiments, for example, to modify the paving materialstructurally to enhance function and/or aesthetics.

An earthy material, such as a soil, can be used as the source of metaloxides. The soil should include metal oxides selected from a groupconsisting of oxides of aluminum, silicon, iron, titanium, cobalt,calcium, magnesium, sodium, and potassium. In some embodiments, themetal oxide can be selected from a group consisting of Al₂O₃, SiO₂,Fe₂O₃, TiO₂, CoO, MgO, Na₂O, K₂O, hydrated forms thereof, orcombinations thereof In some embodiments, the metal oxide can includeAl₂O₃, SiO₂, hydrated forms thereof, or combinations thereof Examples ofhydrated forms of the metal oxides are known to those skilled in theart. Hydrated forms of aluminum oxide include, for example, Al₂O₃.nH₂O,where n can be an integer ranging from 1 to 3.

One of skill in the art will appreciate that earthy materials, such assoil, can be selected from a variety of compositions that are particularto the geographic region of the source. Clay is one of the threeprincipal types of soil, the other two being sand and loam. A certainamount of clay is a desirable constituent of soil, since it binds otherkinds of particles together and retains water. Clay consists of soilparticles the diameters of which are less than 0.005 mm, and alsoconsist of a rock that is composed essentially of clay particles. Impureclays may be used to make bricks, tile, and the cruder types of pottery,while kaolin, or china clay, is required for the finer grades of ceramicmaterials.

In some embodiments, the soil is selected to contain from about 5% toabout 15% organic material by weight. In some embodiments, the soil isselected to contain from about 2% to about 8% organic material byweight. In some embodiments, the soil is selected to contain less thanabout 5% organic material by weight. The composition of the earthymaterial can vary, and component concentrations can be controlled byblending in other components. In some embodiments, the earthy materialscan include 35 to 55 percent clays or argillaceous (clayey) shales, 25to 45 percent quartz, and 25 to 55 percent feldspar. In someembodiments, the earthy material can include about 50% SiO₂ and about40% Al₂O₃. In some embodiments, flint clay can be used as the soil tomake the paving materials of the present invention.

Other additives can be included to control the color of the finishedproduct. The color of the finished product will rely most often in thetypes and amounts of iron oxides present in the raw materials. Colorscan range from a pale yellow to black with light shades of brown to redin-between, depending upon whether an oxidizing or reducing atmosphereexists in the kiln. The color of the metal oxide is adjusted bycontrolling the degree of oxidation.

Examples of metals that form colored oxides include antimony, which canbe used in combination with lead and can form a yellow color; chromiumcan also be used to produce a yellow color; cobalt can be used to form ablue color; copper can be used to form a green or red color; gold can beused to form a purple color; iron can be used to form a yellow, red, orblack color; manganese can be used to form a purple or brown color; andtin can be used to form a white color. Any metal or combination ofmetals known to one of skill in the art can be used to provide a desiredcolor to the final product. It should be appreciated by one of skillthat process variables such as the concentration of the metals and theamount of metal oxidation that results from the heat-treatment should bepreselected carefully to control the color of the final product.

Without intending to be bound by any theory or mechanism of action, theclay portion of a soil can provide the ability to shape the pavingmaterial into a module, i.e. a unit that can be interconnected to form apavement. The quartz (silica) portion of a soil can serve as a fillerand provide strength to the formed module; and, the feldspar portion canserve as a fluxing agent to lower the melting temperatures of the clayand quartz during heat-treatment, sometimes referred to as firing, ofthe paving material. A desirable soil composition can be found directlyin shale deposits, such that blending to obtain these proportions isoften not necessary. In some embodiments, little or no beneficiation, orcrushing and grinding of the mined material, is necessary to prepare acomposition. In most embodiments, however, local clays or shales havinga highly variable composition are used in order to keep transportationcosts as low as possible.

In embodiments using flint clay as the soil and sand as the filler, theflint clay can comprise from about 8-20% of the composition.Accordingly, the sand can comprise most of the remainder of thecomposition, which will comprise about 80-92% of the composition. Otherminor components may be present as impurities in many embodimentswithout affecting the ability of the paving material to perform itsintended use. It should be appreciated that the manufacturingparameters, e.g. filler material, forming pressure, and/or temperature,may need to be adjusted to provide desired performance characteristicsin a paving material formed from these somewhat variable compositions.

Other components known to those of skill in the art can added to holdthe shape of the molded composition in preparation for heat-treatment.Any bonding agent known to one of skill in the art of ceramics can beused. The bonding agent serves as a temporary holding agent to maintainthe desired shape of the composition for the heat-treatment step and canalso enhance bonding within the structure of the final product. Flintclay, for example, can be used as the soil or as a bonding agent forother soils. The flint clay should contain high percentages of silicaand alumina and have few impurities, such as lime, magnesia, soda, andpotash, each of which lower the fusion point of the clay. It should beappreciated that the soil can serve as its own bonding agent to hold theshape of the molded composition together for the heat treatment, wherethe organic component burns away during the heat treatment to leave afused material.

In addition, filler materials are added to the composition and arecarefully selected to assist in the control of the porosity and,accordingly, the permeability of the paving material to aqueous fluids.Any filler material known to one of skill in the art can be used andinclude, but is not limited to, sand and/or gravel. In some embodiments,the filler material can include ceramic particles, glass particles, ormetal oxides.

In some embodiments, the metal oxides can have a melting point that ishigher than the heat-treating temperature used to harden the compositioninto the final product, and such particles can also be added to providethe final product with a non-slip surface by providing protuberances ona traffic bearing surface used for walking or driving. In someembodiments, the filler material can include particles having averagediameters that range from about 1/32 of an inch to about ¼ of an inch,from about 1/16 of an inch to about ¼ of an inch, from about 1/16 of aninch to about ⅛ of an inch, from about ¼ of an inch to about ⅛ of aninch, or any range therein. The particle diameters, and distribution ofparticle diameters can be obtained and designed using particlefractionation methods known in the art.

The composition should be well-mixed in preparation for forming thecomposition into a desired shape. Any method of mixing such acomposition known to one of skill in the art can be used. In someembodiments, the forming of the composition into a desired shape shouldbe done under fairly dry conditions. In these embodiments, the formedcomposition should have a water concentration ranging from about 0.05%to about 10%, from about 1% to about 7%, from about 1% to about 6%, orfrom about 2% to about 5% by weight as the formed composition enters theheat-treating step.

Pressure is applied to the composition to form the desired shape to beheat-treated. The amount of pressure applied can be varied to controlthe average density, as well as the uniformity of the density, of theformed composition. A uniform, or substantially uniform, densitydistribution should be developed across the formed composition to createa final product that is uniform in structure and physicalcharacteristics. Structural characteristics include, but are not limitedto, porosity and shape. Physical characteristics include, but are notlimited to, compressive strength, and permeability. The pressure appliedto form the shape of a composition ranges from about 500 psi to about3000 psi. In some embodiments, the amount of pressure applied to formthe shape of a composition can range from about 700 psi to about 2200psi, from about 1000 psi to about 2000 psi, or any range therein.

Control over the pressure used to form the desired shape from thecomposition provides control over the porosity, permeability, andcompressive strength of the final product. For example, the compressivestrength of the final product increases with an increase in the amountof pressure applied to form the shape of a composition, whereas theporosity of the final product decreases with an increase in pressure.And, a decrease in porosity can result in a decrease in the permeabilityof the final product to aqueous fluids, such as rainwater. Accordingly,one of skill will appreciate that the performance characteristics of thefinal product can be tuned through a careful selection of components fora composition, as well as through a careful selection of the pressureused to form a desired shape from the composition.

The amount of pressure applied to form the shape of a compositiondepends on a variety of factors including, but not limited to, thethickness of the formed composition. The thickness of the final productcan range from about 0.5 inches to about 6.0 inches, from about 1.0 inchto about 5 inches, from about 1.5 inches to about 4 inches, from about2.25 inches to about 4 inches, from about 1.5 inches to about 2.25inches, or any range therein. The pressure applied to the compositioncan be obtained from any molding apparatus known to one of skill in theart.

In some embodiments, a pressure ranging from about 500 psi to about 1000psi can be applied to form the shape of a composition ranging inthickness from about 1.5 inches to about 2.25 inches. In someembodiments, from about 2000 psi to about 3000 psi can be used to formthe shape of a composition ranging in thickness from about 3.0 inches toabout 4.0 inches.

The pressures can be varied to produce different compressive strengths.For example, a 3000 psi pressure can be applied to a 1.5 inch thickcomposition to obtain a high strength as compared to applying a 1000 psipressure to a 2.25 inch thick composition to obtain a higher porosityand relatively lower compressive strength. The general rule, however, isthat to obtain a particular compressive strength from a givencomposition, as the thickness of the desired shape increases, the amountof pressure required to form the shape from the given composition alsoincreases. In most embodiments, the compressive strength can range fromabout 4000 psi to about 12,000 psi, from about 5000 psi to about 10,000psi, from about 6000 psi to about 8000 psi, or any range therein. Insome embodiments, the minimum required compressive strength will rangefrom about 4000 psi to about 5000 psi for light vehicle traffic.

In some embodiments, the paving material can be a formed into a modulehaving a shape that provides an added function, such as enhancing thestructural integrity of the paving surface, providing a non-slip trafficsurface, or providing support for the addition of other structuralcomponents unrelated to paving. In one example, the module can be a unitthat is used in a repetitious juxtaposition with similar components,with components that are not modular, or alone in combination with manyother identical modules to construct a pavement. In another example, themodule can have a shape that is complementary to a component that isused in landscaping, such as a structural brick used in the formation ofa flower bed or some other decorative structure.

A final step in creating the porous, ceramic paving material is theheat-treating step, but the formed composition must be dried to lessthan about 5%, less than about 3%, less than about 1%, or any rangetherein, before entering the heat-treating step in order to preserve thedesired shape and/or physical properties of the paving material. Asdiscussed above, the properties exhibited by the final product can bedesigned by designing the composition in terms of selecting the particlesizes and components, as well as the pressure used to form the desiredshape of the composition.

In addition, the heat-treating temperature contributes to the ultimatemicrostructure of the paving material. In fact, it should be appreciatedthat the selection of temperature and time affects the physicalproperties of a paving module. The temperatures used for heat-treatingin the present invention range from about 1000° C. to about 1500° C.,from about 1100° C. to about 1300° C., from about 1150° C. to about1250° C., or any range therein. At these temperatures, some fillerparticles may not be melted, but the clay or shale ingredients can beselected to contain sufficient impurities to allow for melting andformation of a glass within the composition, thus bonding the particlestogether. The heat-treating time ranges from about 12 hours to about 36hours, from about 18 hours to about 30 hours, from about 22 hours toabout 26 hours, or any range therein.

Crystalline mullite needles can enhance strength by growing into theglassy phase. The resulting microstructure can consist of largesecondary particles embedded in a matrix of fine-grained mullite andglass and can contain a substantial volume of pores. The size and numberof pores is a controllable design parameter that affects the physicalproperties of the paving module. For example, if the heat-treating isinsufficient, the products can have a low strength and poor resistanceto frost and freezing, owing to the presence of many small pores inregions of the paving material. Too much heat-treating can result in theformation of too much glass. The paving material can be strong, but itcan also be brittle and susceptible to failure under mechanical andthermal stress.

FIGS. 2A and 2B illustrate shapes that may be desirable according tosome embodiments of the present invention. FIG. 2A illustrates a pavingmodule. The structural integrity of a paving surface can be enhanced byshaping the paving material into interlocking units 200, i.e. modules,where the units 200 provide resistance to in-plane movement 201, 202 butmay or may not provide resistance to out-of-plane movement 203.Out-of-plane movement 203 would be a relative movement between pavingunits 200 that is in a direction normal or substantially normal to thetraffic surface 204. Examples of interlocking units 200 that provideresistance to out-of-plane movement 203 would include, for example, atongue-in-groove structure as illustrated in FIG. 2B. In someembodiments, a machining step could be added to provide resistance to anout-of-plane movement between paving units by providing such tongue 205and groove 206 structures. In most embodiments, any interlocking designknown to one of skill can be used with the present invention.

FIG. 3 illustrates a method of constructing a porous, ceramic pavementaccording to some embodiments of the present invention. The methodincludes selecting 301 a porous, ceramic paving material having acompressive strength sufficient for a particular use and applying 302the paving material to the surface to be paved. Teachings of how to makesuch a paving material are provided above.

Although not strictly necessary, most embodiments will include selecting303 a base material to serve as a support for the paving material. Thebase material should also be permeable to aqueous fluids. The basematerial is applied 304 to the surface to be paved, and the pavingmaterial is positioned 305 on top of the base material to provide aporous, ceramic pavement.

Factors involved in selecting the porous, ceramic paving material arediscussed above. A factor that should be considered carefully is thethickness of the paving material, since selecting the thickness of thepaving material can include considering structural factors that are notassociated with compressive strength.

In some embodiments, for example, a walking surface can be paved using a1.5 inch thick paving material having a compressive strength thatexceeds 8000 psi. This high amount of compressive strength may beconsidered unnecessary for such a surface, but the thickness may beotherwise necessary for enhancing structural integrity at each jointformed between adjacent modules of the paving material. A thinner pavingmaterial may not provide a sufficient contact area between pavingmodules to provide a paving structure with enough structural integritybetween modules.

Although the paving material can be applied to a surface alone, in manyembodiments, a base material is applied to the surface to provide aproper support and drainage between the paving material and the surfaceto be paved. In some embodiments, the base materials include, but arenot limited to, sand, gravel, or a combination of sand and gravel. Anybase materials known to one of skill in the art can be used, and in someembodiments, the base materials can comprise a combination of layersseparated by a barrier layer to prevent migration of materials betweenthe combination of layers. In some embodiments, the base material can bea scaffolding that forms a support structure between the surface to bepaved and the paving material. This type of base material is commonlyused in the paving of structures that are in locations in which the useof sand and gravel is not practical, such as in the paving of balconies.

EXAMPLES Example 1 Method of Making a Paving Module

Flint clay was the chosen as the soil and sand was chosen as the fillermaterial. The flint clay was combined with the sand at a ratio of about20% soil to about 80% filler. Flint clays can vary in composition, andthe composition of a particular flint clay is particular to the regionfrom which the flint clay was obtained. The flint clay used in thisexample was obtained from Shandong Province, China. Likewise, sand gradeand quality is specific to the region from which it was obtained. Thesand for the filler can be a low grade sand, variable in grit size, andthe sand used in this example was also be obtained from ShandongProvince, China. It should be appreciated that with this variation inmaterial compositions, process parameters such as the filler material,the pressure used to form the desired shape, and the heat-treatingtemperature may need to be adjusted to obtain a desired performancecharacteristic from a particular material composition.

The flint clay and sand was then mixed dry (i.e. ambient air moistureconditions) into a granular form using any mixer available to one ofskill in the art and suitable for mixing soils. A low rpm blade mixerthat turns at about 60-200 rpm was used for the present example. Themixture wa then placed into a mold and pressed into a block form thatwas 20 cm long, 10 cm wide, and 6 cm thick using about 30 metric tons offorce to produce a pressure of about 2200 psi.

The pressed block was then removed from the mold and placed on an ovenrack and dried to under 3% moisture for about 12 hours to about 24 hoursat about 50° C. to about 80° C. The dried, pressed block was then placedinto an oven to heat-treat the block at about 1100° C. for about 24hours to about 48 hours. The time at temperature varies depending on thenumber of paving material modules present in the oven. Normally, theheat-treating time is about 30 hours for a normal set of paving modules.The paving material was found to have a compressive strength of about12,000 psi as measured using the ASTM C-936 method.

Optionally, color is added throughout the composition or as a topcoat. Atopcoat mixture, for example, is added as a 3-6 mm thick surface. Atopcoat may be preferred from a manufacturing standpoint, because itsless expensive to add the coloring as a topcoat as less material isrequired. However, coloring throughout the paving material may bepreferred from a performance standpoint, because a damaged material willnot exhibit a discoloration that would otherwise appear from a chippingof colored topcoat. The topcoat mixture is made the same way, but youadd the metal oxide coloring to the flint clay and the sand. The topcoatmixture is added first as a 3-6 mm layer in the mold, and the bulk ofthe paving module is then added on the topcoat layer. The metal oxidefor coloring can be obtained from Shandong Province, China.

Any grade of sand can be used for the optional color layer, and thesands used for the present invention were obtained from ShandongProvince, China. The coloring layer is often produced from a fine gradeof sand for a more aesthetic appearance. It should be appreciated,however, that the use of a fine sand topcoat will affect thepermeability of the paving to aqueous fluids, such as rain water.Suitable sands can range from about 80 grit to about 200 grit dependingon the smoothness and permeability that is desired.

Example 2 Permeability Testing

A clear plastic tube was glued to the surface of the paving materialmade in Example 1. The clear plastic tube was approximately 2.0 inchesin diameter and about 5.0 inches in height. The tube was filled with 5.0inches of room temperature tap water, such that the tap water wasallowed to permeate the room temperature paving material. The rate ofpermeation was measured.

The permeation rate of a dry paving material was found to be about 2.5inches per minute, whereas the permeation rate of a saturated pavingmaterial was found to be about 1.0 inch per minute. The implementationof a base material was found to enhance permeation, where the basematerial was able to break the surface tension of the aqueous fluid asit exited the paving material, thus assisting in the movement of the tapwater out of the paving material. A base material such as a scaffoldingused in paving a balcony would provide limited contact on the bottomsurface of a paving material, whereas sand would provide a much higherdegree of contact.

While particular embodiments of the present invention have been shownand described, those skilled in the art will note that variations andmodifications can be made to the present invention without departingfrom the spirit and scope of the teachings. One of skill will appreciatethat the teachings have been provided by way of example only and are notintended to limit the scope of the invention.

1. A method of constructing a porous, ceramic pavement comprisingselecting a porous, ceramic paving material having a compressivestrength sufficient for a particular use of a surface to be paved;selecting a base material to serve as a support for the paving material,wherein the base material is permeable to aqueous fluids; applying thebase material to the surface to be paved; and positioning the pavingmaterial on top of the base material to provide a porous, ceramicpavement.
 2. The method of claim 1, wherein the paving material is inthe form of a module having a shape that provides an added function,wherein the function comprises enhancing structural integrity at eachjoint formed by adjacent modules, providing a non-slip surface, orproviding support for the addition of other structural componentsunrelated to paving.
 3. The method of claim 2, wherein the module isinterlocking with itself to provide a resistance to in-plane movement,out-of-plane movement, or a combination thereof.
 4. The method of claim1, wherein the base material comprises sand, gravel, or a combinationthereof.
 5. The method of claim 1, wherein the base material comprises acombination of layers separated by a barrier layer to prevent migrationof materials between the combination of layers.
 6. The method of claim1, wherein the base material comprises a scaffolding to support thepaving material.